The goals of our research program are to identify and understand cellular mechanisms involved in the regulation of placental development. Trophoblast cells are the functional unit of the placenta and their differentiation as gestation progresses is critical for the normal development of the fetus. The differentiation of trophoblast cells is characterized by an alteration in the cell cycle leading to an accumulation of DNA per cell. Nutritional deficiencies and drug abuse have pronounced effects on the development of the placenta and also on the fetus resulting in intrauterine growth retardation. It is presently not known how these environmental agents interfere with placental development. Experiments in Part 1 of this proposal are focused on the characterization of trophoblast differentiation. We are specifically interested in addressing two basic questions: 1) Are the patterns of trophoblast differentiation similar in vivo and in vitro? and 2) Do all trophoblast precursor cells possess the capacity to display the same type of differentiation in vitro? Part 2 of the research project is directed toward determining the involvement of DNA synthesis in the differentiation of trophoblast cells. Part 3 of the proposal is concerned with investigating the regulation of trophoblast differentiation by progesterone. Experiments are designed to examine the site, specificity and temporal characteristics of progesterone's actions. The proposed research relies extensively on analyzing the behavior of trophoblast cells in vitro and on the use of placental lactogen production as a functional, biochemical marker for trophoblast differentiation. Alkaline phosphatase activity and profiles of protein synthesis will also be assessed for their utility as markers for trophoblast differentiation. The experiments use cell culture, column chromatographic, electrophoretic, radioreceptor, and autoradiographic techniques to investigate trophoblast differentiation. The information garnered from these studies promises to advance our understanding of normal placental development and provide new insights regarding the susceptibility of this process to genetic and environmental modifications. Through our studies of trophoblast differentiation we will also generate significant data on the regulation of DNA synthesis and the cell cycle. The rat trophoblast giant cell potentially represents an important tool for studying the control of specific events during the cell cycle.